Multicystic Mesothelioma (MCM)

Multicystic mesothelioma is a rare tumor of the mesothelium, the thin lining of body cavities, that forms clusters of fluid-filled cysts rather than the solid, invasive masses seen in classic malignant mesothelioma. It most often arises in the peritoneum (abdominal lining) of younger women and is generally considered a borderline or low-grade tumor with a much better prognosis than malignant mesothelioma, though it tends to recur locally after surgery.

Origin

First described in detail by Mennemeyer and Smith in 1979, who reported a series of "benign multicystic mesotheliomas" of the peritoneum. The terminology has shifted over the decades, with some pathologists preferring "multilocular peritoneal inclusion cyst" to emphasize its often non-malignant behavior, while others retain "multicystic mesothelioma" because of its tendency to recur.

Significance in Asbestos Context

Unlike the well-known forms of mesothelioma (epithelioid, sarcomatoid, biphasic), multicystic mesothelioma has a debated link to asbestos exposure. Most cases occur in women with prior pelvic surgery, endometriosis, or inflammation, and many patients have no asbestos history at all. For patients diagnosed with MCM, this distinction matters: prognosis is far better than for malignant mesothelioma, but the diagnosis can be confusing on pathology reports and is sometimes initially mistaken for the more aggressive form. If you have been told you have "mesothelioma," it is critical to clarify whether the pathologist means multicystic, well-differentiated papillary, or malignant mesothelioma, because treatment, prognosis, and the strength of any asbestos-related legal claim differ dramatically across these subtypes.

Example Sentence

After her pathology was reviewed at a specialty center, the diagnosis was revised from malignant peritoneal mesothelioma to multicystic mesothelioma, changing both her treatment plan and the trajectory of her case.

Related Terms

Peritoneal Mesothelioma, Well-Differentiated Papillary Mesothelioma, Epithelioid Mesothelioma, Mesothelium, Cytoreductive Surgery, Pathology Second Opinion

Notes

• Request a pathology second opinion at a mesothelioma specialty center (such as MD Anderson, Memorial Sloan Kettering, Brigham and Women's, or a dedicated peritoneal surface malignancy program) before starting any treatment. MCM is rare and easily confused with other cystic lesions and with malignant mesothelioma.
• Ask your pathologist explicitly whether the diagnosis is multicystic mesothelioma, well-differentiated papillary mesothelioma, or malignant (epithelioid/sarcomatoid/biphasic) mesothelioma; the exact wording on the report matters for treatment and for any legal claim.
• Standard treatment is surgical removal of the cysts, sometimes combined with HIPEC (heated intraperitoneal chemotherapy) given the high local recurrence rate; ask whether referral to a peritoneal surface malignancy program is appropriate.
• Preserve all imaging, operative notes, and pathology slides. If recurrence occurs or the diagnosis is later revised, these original materials are essential for re-review.
• Document any occupational, household, or environmental asbestos exposure history even though the link is debated; if exposure exists, it may still be relevant to a claim and to monitoring for other asbestos-related diseases.